Abstract: An activated sludge treatment process and apparatus are provided for denitrification of a trickling filter plant effluent in which the nitrate nitrogen to BOD5 ratio can be maintained at less than or equal to 0.18 without the use of a nitrate monitor to control supplemental dosing with carbonaceous organic compounds or their salts. The apparatus is equipped with a turbidity meter, a phosphate monitor, and with a substrate storage tank for the addition of carbonaceous organic substrate. The substrate is added immediately at the end of the oxic phase and is continued until phosphate release is detected. Accordingly, the phosphate monitor functions as an indicator of nitrate respiration in the anoxic phase.

Abstract: Activated sludge process for biological waste water treatment comprises controlling the supply of oxygen to a single tank reactor in response to the phosphate concentration in the anaerobic phase independent of turbidity. The oxic phase is initiated if the maximum turbidity set point is exceeded in the usual manner. However, if the phosphate concentration exceeds its maximum set point before the turbidity reaches a maximum, then the oxic phase is initiated to end phosphate release. Acetic acid can be added to increase phosphate elimination at the end of the anaerobic phase, prior to switching on the supply of oxygen.

Abstract: A method for biologically removing approximately seventy-five percent of the phosphate contaminants from wastewater comprises controlling the aerator to a single activated sludge tank according to the turbidity of the water and the effluent requirements. Oxic, anoxic, and anaerobic reactions occur sequentially over the entire volume of the single reactor. Greater phosphate removal requires a simultaneous chemical precipitation.

Abstract: A method and apparatus is disclosed for purifying the waste water in an avated sludge-waste water mixture. In dependence upon the state of purification of the waste water, the mixture is ventilated in automatically controlled manner by a gas comprising molecular oxygen. The automatic control of ventilation is exercised by the use of a monitoring device which measures the visible depth of the waste water and, depending upon the measured value, starts-up or switches-off the ventilation.